Resampling circuit, physical quantity sensor unit, inertial measurement unit, and structure monitoring device

ABSTRACT

A resampling circuit converts first data updated synchronously with a first clock signal into second data updated synchronously with a second clock signal asynchronous with the first clock signal and outputs the second data. The resampling circuit measures a first time interval between a plurality of successive edges of the first clock signal, and a second time interval between one of the plurality of edges of the first clock signal and an edge of the second clock signal, with a third clock signal having a higher frequency than the first clock signal and the second clock signal. The resampling circuit calculates and outputs the second data updated at the edge of the second clock signal, based on the first time interval and the second time interval, and a plurality of the first data updated at the plurality of edges of the first clock signal.

The present application is based on and claims priority from JPApplication Serial Number 2018-086189, filed Apr. 27, 2018, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a resampling circuit, a physicalquantity sensor unit, an inertial measurement unit, and a structuremonitoring device.

2. Related Art

An inertial measurement unit (IMU) or a physical quantity sensor unitwhich measures a certain physical quantity such as acceleration orangular velocity converts a signal corresponding to the magnitude of ameasurement target physical quantity from analog to digital, thenperforms various kinds of signal processing such as correction andconversion to generate measurement data, and outputs the measurementdata to an arithmetic processing device (host). Generally, themeasurement data is outputted synchronously with an external triggersignal supplied from the arithmetic processing device asynchronouslywith the sampling rate of A/D conversion, and A/D conversion is carriedout at a higher frequency than the output rate of the measurement data.Therefore, the IMU or physical quantity sensor unit is provided with aresampling circuit which converts the sampling rate at the time of A/Dconversion to the output rate of the measurement data.

JP-A-5-91287 discloses a technique of converting a sampling rate byperforming interpolation with the lowest common multiple of two samplingrates, then smoothing via a digital filter, and decimating the result.

JP-A-5-91287 is an example of the related art.

However, in the technique disclosed in JP-A-5-91287, when two samplingrates are asynchronous, a periodic noise may be generated in output datadue to a periodic resampling error.

SUMMARY

A resampling circuit according to an aspect of the present disclosure isa resampling circuit that converts first data updated synchronously witha first clock signal into second data updated synchronously with asecond clock signal asynchronous with the first clock signal and outputsthe second data. The resampling circuit measures a first time interval,which is a time interval between a plurality of successive edges of thefirst clock signal, and a second time interval, which is a time intervalbetween one of the plurality of edges of the first clock signal and anedge of the second clock signal, with a third clock signal having ahigher frequency than the first clock signal and the second clocksignal. The resampling circuit calculates and outputs the second dataupdated at the edge of the second clock signal, based on the first timeinterval and the second time interval, and a plurality of the first dataupdated at the plurality of edges of the first clock signal.

In the resampling circuit according to the aspect of the presentdisclosure, a first edge of the plurality of edges of the first clocksignal may occur before the edge of the second clock signal. A secondedge of the plurality of edges of the first clock signal may occur afterthe edge of the second clock signal. The second time interval may be atime interval between the first edge and the edge of the second clocksignal.

In the resampling circuit according to the aspect of the presentdisclosure, a first edge of the plurality of edges of the first clocksignal may occur before the edge of the second clock signal. A secondedge of the plurality of edges of the first clock signal may occur afterthe first edge and before the edge of the second clock signal. Thesecond time interval may be a time interval between the second edge andthe edge of the second clock signal.

In the resampling circuit according to the aspect of the presentdisclosure, the second data updated at the edge of the second clocksignal may be calculated by approximation based on a relation betweenthe first time interval and the second time interval, and a plurality ofthe first data updated at the plurality of edges of the first clocksignal.

In the resampling circuit according to the aspect of the presentdisclosure, the approximation may be linear approximation.

The resampling circuit according to the aspect of the present disclosuremay include a low-pass filter which outputs the first data. A cutofffrequency of the low-pass filter may be lower than a Nyquist frequencyof the second clock signal.

In the resampling circuit according to the aspect of the presentdisclosure, the first clock signal may be a sampling clock in A/Dconversion.

In the resampling circuit according to the aspect of the presentdisclosure, the second clock signal may be a trigger signal inputtedfrom outside to the resampling circuit.

A physical quantity sensor unit according to an aspect of the presentdisclosure includes: the resampling circuit of one of the foregoingconfigurations; and a physical quantity sensor.

In the physical quantity sensor unit according to the aspect of thepresent disclosure, the physical quantity sensor may detect at least oneof acceleration and angular velocity.

An inertial measurement unit according to an aspect of the presentdisclosure includes: a physical quantity sensor which detects at leastone of acceleration and angular velocity; a signal processing circuitwhich includes the resampling circuit of one of the foregoingconfigurations and processes a signal outputted from the physicalquantity sensor; and a communication circuit which transmits inertialdata resulting from the processing by the signal processing circuit tooutside.

A structure monitoring device according to an aspect of the presentdisclosure includes: the physical quantity sensor unit of one of theforegoing configurations; a receiver which receives a detection signalfrom the physical quantity sensor unit installed on a structure; and acalculator which calculates an angle of inclination of the structure,based on a signal outputted from the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an outline of processing in a resampling circuitaccording to a first embodiment.

FIG. 2 shows an example of the configuration of the resampling circuitaccording to the first embodiment.

FIG. 3 shows an example of a characteristic of a low-pass filter and acharacteristic of averaging.

FIG. 4 illustrates an outline of processing in a resampling circuitaccording to a second embodiment.

FIG. 5 shows an example of the configuration of the resampling circuitaccording to the second embodiment.

FIG. 6 illustrates an outline of processing in a resampling circuitaccording to a third embodiment.

FIG. 7 shows an example of the configuration of the resampling circuitaccording to the third embodiment.

FIG. 8 illustrates an outline of processing in a resampling circuitaccording to a fourth embodiment.

FIG. 9 shows an example of the configuration of the resampling circuitaccording to the fourth embodiment.

FIG. 10 is a perspective view showing an outline of a physical quantitysensor unit.

FIG. 11 is an exploded perspective view of the physical quantity sensorunit.

FIG. 12 is a perspective view illustrating a schematic configuration ofan acceleration sensor element.

FIG. 13 is a cross-sectional view illustrating a schematic configurationof an acceleration detector using the acceleration sensor element.

FIG. 14 is a perspective exterior view showing the configuration of acircuit board of an inertial measurement unit according to anembodiment.

FIG. 15 shows the configuration of a structure monitoring deviceaccording to an embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present disclosure will now be described in detailwith reference to the drawings. The embodiments described below shouldnot unduly limit the content of the present disclosure described in theappended claims. Not all the elements described below are essentialelements of the present disclosure.

1. Resampling Circuit

Hereinafter, each embodiment is described, taking, as an example, aresampling circuit which has an A/D-converted measurement target signal,converts digital data (hereinafter referred to as “AD data”) updatedsynchronously with a sampling clock (hereinafter referred to as “ADclock”) in the A/D conversion into measurement data updatedsynchronously with an externally inputted trigger signal (hereinafterreferred to as “external trigger”) asynchronous with the AD clock, andoutputs the measurement data. The A/D conversion of the measurementtarget signal may be, for example, converting the voltage of themeasurement target signal into digital data or converting the frequencyof the measurement target signal into digital data. The resamplingcircuit converts the AD data into the measurement data, using a clock(hereinafter referred to as “high-frequency clock”) having a higherfrequency than the AD clock and the external trigger. In the descriptionbelow, the external trigger and the AD clock are asynchronous with eachother. The frequency of the AD clock is higher than the frequency of theexternal trigger. The frequency of the high-frequency clock issufficiently higher than the frequency of the AD clock. Thehigh-frequency clock may be synchronous or asynchronous with the ADclock or the external trigger.

The AD clock is an example of the “first clock signal” according to thepresent disclosure. The external trigger is an example of the “secondclock signal” according to the present disclosure. The high-frequencyclock is an example of the “third clock signal” according to the presentdisclosure. The AD data is an example of the “first data” according tothe present disclosure. The measurement data is an example of the“second data” according to the present disclosure.

1-1. First Embodiment

FIG. 1 illustrates an outline of processing in a resampling circuitaccording to a first embodiment. In FIG. 1, an edge of an external clockcomes every period T1 and an edge of an AD clock comes every period T2.An edge B₁ of the external trigger comes between two successive edgesA₂, A₃ of the AD clock. The edge A₂ occurs before the edge B₁. The edgeA₃ occurs after the edge B₁. An edge B₂ of the external trigger comesbetween two successive edges A₄, As of the AD clock. The edge A₄ occursbefore the edge B₂. The edge A₅ occurs after the edge B₂. Similarly, anedge B₃ of the external trigger comes between two successive edges A₆,A_(v) of the AD clock. The edge A_(g) occurs before the edge B₃. Theedge A₇ occurs after the edge B₃. The edges A₂, A₄, A₆ are an example ofthe “first edge” according to the present disclosure. The edges A₃, As,A₇ are an example of the “second edge” according to the presentdisclosure.

The resampling circuit of the first embodiment calculates a resampledvalue DO_(i) at an edge B_(i) by the following interpolation-basedlinear approximation formula (1), based on the relation between a firsttime interval n_(k)+m_(k), which is the time interval between twosuccessive edges A_(k), A_(k+1) of the AD clock with an edge B_(i) ofthe external trigger coming in-between, and a second time intervaln_(k), which is the time interval between the edge A_(k) and the edgeB_(i), and two values D_(k), D_(k+1) of the AD data updated at the twoedges A_(k), A_(k+1).

$\begin{matrix}{{DO}_{i} = {D_{k} + {\left( {D_{k + 1} - D_{k}} \right) \times \frac{n_{k}}{n_{k} + m_{k}}}}} & (1)\end{matrix}$

The resampling circuit of the first embodiment then outputs measurementdata having resampled values DO₁, DO₂, DO₃, . . . every period T1 of theexternal trigger.

FIG. 2 shows an example of the configuration of the resampling circuitof the first embodiment. As shown in FIG. 2, a resampling circuit 1 ofthe first embodiment includes a low-pass filter 10, a latch 12, a delay(Z⁻¹) 20, a latch 22, a counter 30, a latch 32, a delay (Z⁻¹) 40, alatch 42, a linear approximator 50, a timing generator 60, and an ORcircuit 70.

To the low-pass filter (LPF) 10, AD data resulting from A/D-converting ameasurement target signal by an A/D converter 2 outside the resamplingcircuit 1 is inputted. The low-pass filter 10 filters the AD data andthus damps a high-range noise. For example, the low-pass filter 10 isimplemented by a digital filter such as a FIR (finite impulse response)filter or IIR (infinite impulse response) filter.

The latch 12 takes in and holds the AD data outputted from the low-passfilter 10 at every edge of the AD clock. The edge of the AD clock atwhich the latch 12 takes in the data may be a rising edge or a fallingedge according to need. For example, the latch 12 is implemented by aregister made up of a predetermined number of D flip-flops.

The delay 20 delays the data held by the latch 12 and outputs thedelayed data. The latch 22 takes in and holds the data outputted fromthe delay 20 at every edge of the AD clock. The edge of the AD clock atwhich the latch 22 takes in the data may be the same as the edge of theAD clock at which the latch 12 takes in the data. For example, the delay20 and the latch 22 are implemented by a register made up of apredetermined number of D flip-flops.

The OR circuit 70 has the external trigger and the AD clock inputtedthereto and outputs an OR signal of these.

The counter 30 counts the number of edges of the high-frequency clockwhen a reset signal from the latch 32 is inactive (for example,low-level). The counter 30 initializes the count value to zero when thereset signal from the latch 32 is active (for example, high-level). Thecounter 30 may count the number of rising edges of the high-frequencyclock, the number of falling edges of the high-frequency clock, or thenumber of rising edges and falling edges of the high-frequency clock,according to need.

The latch 32 takes in and holds the count value from the counter 30 atevery edge of the OR signal outputted from the OR circuit 70, that is,every time an edge of the external trigger or an edge of the AD clockcomes. The latch 32 also turns the reset signal active for apredetermined time and supplies the reset signal to the counter 30. Forexample, the latch 32 is implemented by a register made up of apredetermined number of D flip-flops.

The delay 40 delays the value held by the latch 32 and outputs thedelayed value. The latch 42 takes in and holds the value outputted fromthe delay 40 at every edge of the OR signal outputted from the ORcircuit 70. For example, the delay 40 and the latch 42 are implementedby a register made up of a predetermined number of D flip-flops.

The timing generator 60 outputs a control signal which turns active fora predetermined time after the timing of an edge of the AD clockfollowing the arrival of an edge of the external trigger. In the exampleof FIG. 1, the control signal turns active at the edges edge A₃, A₅, A₇,. . . of the AD clock.

The linear approximator 50 carries out linear approximation using theformula (1), based on the relation between the values held respectivelyby the latches 32, 42 and the values of the data held by the latches 12,22, and updates the output value at the timing when the control signaloutputted from the timing generator 60 turns active. In the example ofFIG. 1, at the edge A_(k+1) of the AD clock following the arrival of theedge B_(i) of the external trigger, the value of the data held by thelatch 22 is updated to D_(k) and the value of the data held by the latch12 is updated to D_(k+1). Also, at the edge A_(k+1) of the AD clock, thevalue held by the latch 42 is updated to n_(k) and the value held by thelatch 32 is updated to m_(k). After the edge A_(k+1) of the AD clock,the output value from the linear approximator 50 is updated to the valueDO_(i) obtained by the linear approximation formula (1).

FIG. 3 shows an example of a characteristic of the low-pass filter 10and a characteristic of smoothing in which the resampled value iscalculated based on the AD data outputted from the low-pass filter 10.In FIG. 3, the horizontal axis represents frequency and the verticalaxis represents gain. The characteristic (LPF characteristic) of thelow-pass filter 10 is indicated by a solid line. The characteristic ofsmoothing (smoothing characteristic) is indicated by a chain-dashedline. As shown in FIG. 3, to reduce a folding noise in the frequencyband of the smoothed signal in the resampling based on the externaltrigger, the cutoff frequency of the low-pass filter 10 is set to belower than half the frequency of the external trigger (Nyquistfrequency). The pass range of the low-pass filter 10 limits thefrequency band of the measurement data outputted from the resamplingcircuit 1.

In the related-art technique, for example, in the foregoing IMU orphysical quantity sensor, when a clock signal for A/D conversion and anexternal trigger signal are asynchronous with each other, a periodicnoise may be generated in output data due to a periodic resamplingerror, resulting in lower quality of measurement data.

In contrast, the resampling circuit 1 of the first embodiment having theforegoing configuration according to the present disclosure measures afirst time interval, which is the time interval between two successiveedges of the AD clock, and a second time interval, which is the timeinterval between one of the two edges of the AD clock and an edge of theexternal trigger, with a high-frequency clock having a higher frequencythan the AD clock and the external trigger. The resampling circuit 1 ofthe first embodiment then calculates and outputs measurement dataupdated at the edge of the external trigger, based on the first timeinterval and the second time interval thus measured, and the two AD dataupdated at the two edges of the AD clock. Specifically, the measurementdata updated at the edge of the external trigger is calculated by linearapproximation based on the relation between the first time interval andthe second time interval thus measured, and the two AD data updated atthe two edges of the AD clock. Thus, the resampling circuit 1 of thefirst embodiment, which asynchronously resamples the AD data in responseto the external trigger, smoothes the AD data near the edge of theexternal trigger to generate measurement data and therefore can reduce aperiodic noise generated in the resampled measurement data.

Also, in the resampling circuit 1 of the first embodiment, the low-passfilter 10 limits the band of the measurement data. Therefore, the ADdata outputted from the low-pass filter 10 has a high correlation aroundthe point when the AD data is updated synchronously with an edge of theAD clock, and the error due to linear approximation is reduced. Thus,measurement data is acquired with high accuracy.

Moreover in the resampling circuit 1 of the first embodiment, the ADclock having a higher frequency than the external trigger can form afilter and therefore the low-pass filter 10 having a high degree offreedom in filter shape limits the band of the measurement data. Thisreduces the constraint on the design of a band-limiting filter providedon the stage subsequent to the resampling circuit 1 and can reduce thecircuit area of the band-limiting filter. Thus, for example, making thepass range of the low-pass filter 10 equal to the pass range of theband-limiting filter to be provided on the stage subsequent to theresampling circuit enables omission of the band-limiting filter.

1-2. Second Embodiment

FIG. 4 illustrates an outline of processing in a resampling circuitaccording to a second embodiment. In FIG. 4, an edge of an externalclock comes every period T1 and an edge of an AD clock comes everyperiod T2. Of two successive edges A₁, A₂ of the AD clock, the edge A₁occurs before an edge B₁ of the external trigger, and the edge A₂ occursafter the edge A₁ and before the edge B₁. Of two successive edges A₃, A₄of the AD clock, the edge A₃ occurs before an edge B₂ of the externaltrigger, and the edge A₄ occurs after the edge A₃ and before the edgeB₂. Similarly, of two successive edges A₅, A₆ of the AD clock, the edgeA₅ occurs before an edge B₃ of the external trigger, and the edge A₆occurs after the edge A₅ and before the edge B₃. The edges A₁, A₃, A₅are an example of the “first edge” according to the present disclosure.The edges A₂, A₄, A₆ are an example of the “second edge” according tothe present disclosure.

The resampling circuit of the second embodiment regards the timeinterval between two successive edges A_(k), A_(k+1) of the AD clockwith an edge B_(i) of the external trigger coming in-between, as equalto a first time interval n_(k−1), which is the time interval between twoedges A_(k−1), A_(k) of the AD clock, and calculates a resampled valueDO_(i) at the edge B_(i) by the following extrapolation-based linearapproximation formula (2), based on the relation between the first timeinterval n_(k−1) and a second time interval m_(k), which is the timeinterval between the edge A_(k) and the edge B_(i), and two valuesD_(k−1), D_(k) of the AD data updated at the two edges A_(k−1), A_(k).

$\begin{matrix}{{DO}_{i} = {D_{k} + {\left( {D_{k} - D_{k - 1}} \right) \times \frac{m_{k}}{n_{k - 1}}}}} & (2)\end{matrix}$

The resampling circuit of the second embodiment then outputs measurementdata having resampled values DO₁, DO₂, DO₃, . . . every period T1 of theexternal trigger.

FIG. 5 shows an example of the configuration of the resampling circuitof the second embodiment. In FIG. 5, components similar to those in FIG.2 are denoted by the same reference signs. In the description below, theexplanation of components similar to those in the first embodiment isomitted or simplified. As shown in FIG. 5, a resampling circuit 1 of thesecond embodiment includes a low-pass filter 10, a latch 12, a delay(Z⁻¹) 20, a latch 22, a counter 30, a latch 32, a delay (Z⁻¹) 40, alatch 42, a linear approximator 50, and an OR circuit 70.

The configurations and operations of the low-pass filter 10, the latches12, 22, 32, 42, the delays 20, 40, the counter 30, and the OR circuit 70are similar to those in the first embodiment and therefore will not bedescribed further.

The linear approximator 50 carries out linear approximation using theformula (2), based on the relation between the values held respectivelyby the latches 32, 42 and the values of the data held by the latches 12,22, and updates the output value after the edge of the external trigger.In the example of FIG. 4, at the edge B_(i) of the external trigger, thevalue of the data held by the latch 22 is D_(k−1) and the value of thedata held by the latch 12 is D_(k). Also, at the edge B_(i) of theexternal trigger, the value held by the latch 42 is updated to n_(k−1)and the value held by the latch 32 is updated to m_(k). After the edgeB_(i) of the external trigger, the output value from the linearapproximator 50 is updated to the value DO_(i) obtained by the linearapproximation formula (2).

With such a configuration, the resampling circuit 1 of the secondembodiment measures a first time interval, which is the time intervalbetween two successive edges of the AD clock, and a second timeinterval, which is the time interval between one of the two edges of theAD clock and an edge of the external trigger, with a high-frequencyclock having a higher frequency than the AD clock and the externaltrigger. The resampling circuit 1 of the second embodiment thencalculates and outputs measurement data updated at the edge of theexternal trigger, based on the first time interval and the second timeinterval thus measured, and the two AD data updated at the two edges ofthe AD clock. Specifically, the measurement data updated at the edge ofthe external trigger is calculated by linear approximation based on therelation between the first time interval and the second time intervalthus measured, and the two AD data updated at the two edges of the ADclock. Thus, the resampling circuit 1 of the second embodiment, whichasynchronously resamples the AD data in response to the externaltrigger, smoothes the AD data near the edge of the external trigger togenerate measurement data and therefore can reduce a periodic noisegenerated in the resampled measurement data.

Also, the resampling circuit 1 of the second embodiment can achieveeffects similar to those of the resampling circuit 1 of the firstembodiment.

Moreover, in the resampling circuit 1 of the second embodiment, when anedge of the external trigger comes, linear approximation can be carriedout without having to wait for the next edge of the AD clock. Therefore,the delay time until the measurement data is outputted after theexternal trigger is inputted can be made shorter than in the resamplingcircuit 1 of the first embodiment.

1-3. Third Embodiment

FIG. 6 illustrates an outline of processing in a resampling circuitaccording to a third embodiment. In FIG. 6, an edge of an external clockcomes every period T1 and an edge of an AD clock comes every period T2.An edge B₁ of the external trigger comes between two edges A₂, A₃, ofthree successive edges A₁, A₂, A₃ of the AD clock. The two edges A₁, A₂occur before the edge B₁. The edge A₃ occurs after the edge B₁. An edgeB₂ of the external trigger comes between two edges A₄, A₅, of threesuccessive edges A₃, A₄, As of the AD clock. The two edges A₃, A₄ occurbefore the edge B₂. The edge A₅ occurs after the edge B₂. Similarly, anedge B₃ of the external trigger comes between two edges A₆, A₇, of threesuccessive edges A₅, A₆, A₇ of the AD clock. The two edges A₅, A₆ occurbefore the edge B₃. The edge A₇ occurs after the edge B₃. The edges A₂,A₄, A_(g) are an example of the “first edge” according to the presentdisclosure. The edges A₃, A₅, A₇ are an example of the “second edge”according to the present disclosure.

The resampling circuit of the third embodiment calculates a resampledvalue DO_(i) at an edge B_(i) by interpolation-based linearapproximation, based on the relation between a first time intervaln_(k−1), which is the time interval between two successive edgesA_(k−1), A_(k) of three successive edges A_(k−1), A_(k), A_(k+1) of theAD clock with an edge B_(i) of the external trigger coming in-between, afirst time interval n_(k)+m_(k), which is the time interval between thetwo edges A_(k), A_(k+1), a second time interval n_(k), which is thetime interval between the edge A_(k) and the edge B_(i), and threevalues D_(k−1), D_(k), D_(k+1) of the AD data updated at the three edgesA_(k−1), A_(k), A_(k+1). For example, the least squares method or thelike can be used as a method of linear approximation. The resamplingcircuit of the third embodiment then outputs measurement data havingresampled values DO₁, DO₂, DO₃, every period T1 of the external trigger.

FIG. 7 shows an example of the configuration of the resampling circuitof the third embodiment. In FIG. 7, components similar to those in FIG.2 are denoted by the same reference signs. In the description below, theexplanation of components similar to those in the first embodiment isomitted or simplified. As shown in FIG. 7, a resampling circuit 1 of thethird embodiment includes a low-pass filter 10, a latch 12, a delay(Z⁻¹) 20, a latch 22, a counter 30, a latch 32, a delay (Z⁻¹) 40, alatch 42, a linear approximator 50, a timing generator 60, an OR circuit70, a delay (Z⁻¹) 80, a latch 82, a delay (Z⁻¹) 90, and a latch 92.

The configurations and operations of the low-pass filter 10, the latch12, the delay 20, the latch 22, the counter 30, the latch 32, the delay40, the latch 42, and the OR circuit 70 are similar to those in thefirst embodiment and therefore will not be described further.

The delay 80 delays the data held by the latch 22 and outputs thedelayed data. The latch 82 takes in and holds the data outputted fromthe delay 80 at every edge of the AD clock. The edge of the AD clock atwhich the latch 82 takes in the data may be the same as the edge of theAD clock at which the latches 12, 22 take in the data. For example, thedelay 80 and the latch 82 are implemented by a register made up of apredetermined number of D flip-flops.

The delay 90 delays the value held by the latch 42 and outputs thedelayed value. The latch 92 takes in and holds the value outputted fromthe delay 90, at every edge of the OR signal outputted from the ORcircuit 70. For example, the delay 90 and the latch 92 are implementedby a register made up of a predetermined number of D flip-flops.

The linear approximator 50 carries out linear approximation based on therelation between the values held respectively by the latches 32, 42, 92and the values of the data held by the latches 12, 22, 82 and updatesthe output value at the timing when the control signal outputted fromthe timing generator 60 turns active. In the example of FIG. 6, at theedge A_(k+1) of the AD clock following the arrival of the edge B_(i) ofthe external trigger, the value of the data held by the latch 82 isupdated to D_(k−1), the value of the data held by the latch 22 isupdated to D_(k), and the value of the data held by the latch 12 isupdated to D_(k+1). Also, at the edge A_(k+1) of the AD clock, the valueheld by the latch 92 is updated to n_(k−1), the value held by the latch42 is updated to n_(k), and the value held by the latch 32 is updated tom_(k). After the edge A_(k+1) of the AD clock, the output value from thelinear approximator 50 is updated to the value DO_(i) obtained by linearapproximation.

With such a configuration, the resampling circuit 1 of the thirdembodiment measures two first time intervals, which are the timeintervals between three successive edges of the AD clock, and a secondtime interval, which is the time interval between one of the three edgesof the AD clock signal and an edge of the external trigger, with ahigh-frequency clock having a higher frequency than the AD clock and theexternal trigger. The resampling circuit 1 of the third embodiment thencalculates and outputs measurement data updated at the edge of theexternal trigger, based on the two first time intervals and the secondtime interval thus measured, and the three AD data updated at the threeedges of the AD clock. Specifically, the measurement data updated at theedge of the external trigger is calculated by linear approximation basedon the relation between the two first time intervals and the second timeinterval thus measured, and the three AD data updated at the three edgesof the AD clock. Thus, the resampling circuit 1 of the third embodiment,which asynchronously resamples the AD data in response to the externaltrigger, smoothes the AD data near the edge of the external trigger togenerate measurement data and therefore can reduce a periodic noisegenerated in the resampled measurement data.

Also, the resampling circuit 1 of the third embodiment can achieveeffects similar to those of the resampling circuit 1 of the firstembodiment.

1-4. Fourth Embodiment

FIG. 8 illustrates an outline of processing in a resampling circuitaccording to a fourth embodiment. In FIG. 8, an edge of an externalclock comes every period T1 and an edge of an AD clock comes everyperiod T2. Of three successive edges A₀, A₁, A₂ (edge A₀ not beingillustrated) of the AD clock, two edges A₀, A₁ occur before an edge B₁of the external trigger, and the edge A₂ occurs after the edge A₁ andbefore the edge B₁. Of three successive edges A₂, A₃, A₄ of the ADclock, two edges A₂, A₃ occur before an edge B₂ of the external trigger,and the edge A₄ occurs after the edge A₃ and before the edge B₂.Similarly, of three successive edges A₄, A₅, A₆ of the AD clock, twoedges A₄, A₅ occur before an edge B₃ of the external trigger, and theedge A₆ occurs after the edge A₅ and before the edge B₃. The edges A₁,A₃, A₅ are an example of the “first edge” according to the presentdisclosure. The edges A₂, A₄, A₆ are an example of the “second edge”according to the present disclosure.

The resampling circuit of the fourth embodiment regards the timeinterval between two successive edges A_(k), A_(k+1) of the AD clockwith an edge B_(i) of the external trigger coming in-between, as equalto a first time interval n_(k−1), which is the time interval between twoedges A_(k−1), A_(k) of the AD clock, and calculates a resampled valueDO_(i) at the edge B_(i) by extrapolation-based linear approximation,based on the relation between a first time interval n_(k−2), which isthe time interval between two edges A_(k−2), A_(k−1) of the AD clock,the first time interval n_(k−1), a second time interval m_(k), which isthe time interval between the edge A_(k) and the edge B_(i), and threevalues D_(k−2), D_(k−1), D_(k) of the AD data updated at the three edgesA_(k−2), A_(k−1), A_(k). For example, the least squares method or thelike can be used as a method of linear approximation. The resamplingcircuit of the fourth embodiment then outputs measurement data havingresampled values DO₁, DO₂, DO₃, . . . every period T1 of the externaltrigger.

FIG. 9 shows an example of the configuration of the resampling circuitof the fourth embodiment. In FIG. 9, components similar to those in FIG.7 are denoted by the same reference signs. In the description below, theexplanation of components similar to those in the third embodiment isomitted or simplified. As shown in FIG. 9, a resampling circuit 1 of thefourth embodiment includes a low-pass filter 10, a latch 12, a delay(Z⁻¹) 20, a latch 22, a counter 30, a latch 32, a delay (Z⁻¹) 40, alatch 42, a linear approximator 50, an OR circuit 70, a delay (Z⁻¹) 80,a latch 82, a delay (Z⁻¹) 90, and a latch 92.

The configurations and operations of the low-pass filter 10, the latches12, 22, 32, 42, 82, 92, the delays 20, 40, 80, 90, the counter 30, andthe OR circuit 70 are similar to those in the third embodiment andtherefore will not be described further.

The linear approximator 50 carries out linear approximation based on therelation between the values held respectively by the latches 32, 42, 92and the values of the data held by the latches 12, 22, 82 and updatesthe output value after the edge of the external trigger. In the exampleof FIG. 8, at the edge B_(i) of the external trigger, the value of thedata held by the latch 82 is D_(k−2), the value of the data held by thelatch 22 is D_(k−1), and the value of the data held by the latch 12 isD_(k). Also, at the edge B_(i) of the external trigger, the value heldby the latch 92 is updated to n_(k−2), the value held by the latch 42 isupdated to n_(k−1), and the value held by the latch 32 is updated tom_(k). After the edge B_(i) of the external trigger, the output valuefrom the linear approximator 50 is updated to the value DO_(i) obtainedby linear approximation.

With such a configuration, the resampling circuit 1 of the fourthembodiment measures two first time intervals, which are the timeintervals between three successive edges of the AD clock, and a secondtime interval, which is the time interval between one of the three edgesof the AD clock signal and an edge of the external trigger, with ahigh-frequency clock having a higher frequency than the AD clock and theexternal trigger. The resampling circuit 1 of the fourth embodiment thencalculates and outputs measurement data updated at the edge of theexternal trigger, based on the two first time intervals and the secondtime interval thus measured, and the three AD data updated at the threeedges of the AD clock. Specifically, the measurement data updated at theedge of the external trigger is calculated by linear approximation basedon the relation between the two first time intervals and the second timeinterval thus measured, and the three AD data updated at the three edgesof the AD clock. Thus, the resampling circuit 1 of the fourthembodiment, which asynchronously resamples the AD data in response tothe external trigger, smoothes the AD data near the edge of the externaltrigger to generate measurement data and therefore can reduce a periodicnoise generated in the resampled measurement data.

Also, the resampling circuit 1 of the fourth embodiment can achieveeffects similar to those of the resampling circuit 1 of the secondembodiment.

2. Physical Quantity Sensor Unit

A physical quantity sensor unit according to this embodiment includesthe resampling circuit 1 of the foregoing embodiments and a physicalquantity sensor which outputs a measurement target signal. The physicalquantity sensor unit outputs packet data including detection data of aphysical quantity, synchronously with an external trigger supplied froman arithmetic processing device (host). The physical quantity sensordetects at least one of acceleration and angular velocity as a physicalquantity. In the description below, a physical quantity sensor unit 100having a physical quantity sensor which is an acceleration sensor fordetecting acceleration as a physical quantity is described as anexample.

FIG. 10 is a perspective view showing the configuration of the physicalquantity sensor unit 100 as viewed from an installation target surfacewhere the physical quantity sensor unit 100 is fixed. In the descriptionbelow, an axis along the long sides of the physical quantity sensor unit100, which is rectangular as viewed in a plan view, is defined as anX-axis. An axis orthogonal to the X-axis as viewed in a plan view isdefined as a Y-axis. An axis along the thickness of the physicalquantity sensor unit 100 is defined as a Z-axis.

The physical quantity sensor unit 100 is a rectangular parallelepipedhaving a rectangular planar shape. The physical quantity sensor unit 100is, for example, approximately 50 mm long on the long sides along theX-axis, approximately 24 mm long on the short sides along the Y-axisorthogonal to the X-axis, and approximately 16 mm thick. The physicalquantity sensor unit 100 has a screw hole 103 formed at two positionsnear both ends of one long side and at one position in a center part ofthe other long side. The physical quantity sensor unit 100 is used inthe state of being fixed to an installation target surface of aninstallation target object (device) of a structure such as a bridge orbulletin board, with a fixing screw inserted in each of the three screwholes 103.

As shown in FIG. 10, an opening 121 is provided on a surface of thephysical quantity sensor unit 100 as viewed from the installation targetsurface. A plug-type connector 116 is arranged inside the opening 121.The connector 116 has a plurality of pins arranged in two lines. In eachline, a plurality of pins is arrayed along the Y-axis. A socket-typeconnector, not illustrated, is coupled to the connector 116 from theinstallation target object. This allows transmission and reception of adrive voltage of the physical quantity sensor unit 100 and an electricalsignal such as detection data.

FIG. 11 is an exploded perspective view of the physical quantity sensorunit 100. As shown in FIG. 11, the physical quantity sensor unit 100 ismade up of a container 101, a lid 102, a seal member 141, and a circuitboard 115 or the like. More specifically, in the physical quantitysensor unit 100, the circuit board 115 is installed inside the container101 via a fixing member 130, and the opening of the container 101 iscovered with the lid 102 via the seal member 141 having a shockabsorbing property.

The container 101 is, for example, an accommodation container for thecircuit board 115, made of aluminum and molded into the shape of a boxhaving an internal space. The container 101 can be formed by slicing ordie-casting (metal mold casting) aluminum. The material of the container101 is not limited to aluminum and may be other metals such as zinc orstainless steel or may be a resin or a composite material of a metal anda resin. The outer shape of the container 101 is a rectangularparallelepiped having a substantially rectangular planar shape,similarly to the overall shape of the physical quantity sensor unit 100.The container 101 has a fixing protrusion 104 provided at two positionsnear both ends of one long side and at one position in a center part ofthe other long side. The screw hole 103 is formed in each of the fixingprotrusions 104. The fixing protrusion 104 provided at the two positionsnear both ends of the one long side is substantially triangular asviewed in a plan view, including an intersection part between the shortside and the long side. The fixing protrusion 104 provided at the oneposition in the center part of the other long side is substantiallytrapezoidal, facing the internal space of the container 101 as viewed ina plan view.

The container 101 is in the shape of a box having arectangular-parallelepiped outer shape and opening to one side. Theinside of the container 101 is an internal space (accommodation space)surrounded by a bottom wall 112 and a sidewall 111. In other words, thecontainer 101 is in the shape of a box where one face opposite thebottom wall 112 is an opening face 123. The outer edge of the circuitboard 115 is arranged (accommodated) along an inner surface 122 of thesidewall 111. The lid 102 is fixed to cover the opening. The openingface 123 opposite the bottom wall 112 is the face where the lid 102 isplaced. On the opening face 123, the fixing protrusion 104 is providedupright at the two positions near both ends of the one long side of thecontainer 101 and at the one position in the center part of the otherlong side. The top surface (surface exposed in the −Z direction) of thefixing protrusion 104 is flush with the top surface of the container101.

In the internal space of the container 101, a protrusion 129 protrudinginto the internal space from the sidewall 111 over a range from thebottom wall 112 to the opening face 123 is provided in a center part ofthe one long side opposite the fixing protrusion 104 provided in thecenter part of the other long side. A female screw 174 is provided onthe top surface (flush with the opening face 123) of the protrusion 129.The lid 102 is fixed to the container 101 via the seal member 141, witha screw 172 inserted in a penetration hole 176 and the female screw 174.The fixing protrusion 104 provided in the center part of the other longside may protrude into the internal space from the sidewall 111 over arange from the bottom wall 112 to the opening face 123, similarly to theprotrusion 129. The protrusion 129 and the fixing protrusion 104 areprovided at positions facing constricted parts 133, 134 of the circuitboard 115, described later.

In the internal space of the container 101, a first pedestal 127 and asecond pedestal 125 protruding in the form of a step rising from thebottom wall 112 toward the opening face 123 are provided. The firstpedestal 127 is provided at a position facing the arrangement area ofthe plug-type (male) connector 116 installed on the circuit board 115and is provided with the opening 121 (see FIG. 10) where the plug-type(male) connector 116 is inserted. The first pedestal 127 functions as apedestal for fixing the circuit board 115 to the container 101. Theopening 121 penetrates the container 101 from the inside (inner side) tothe outside.

The second pedestal 125 is located on the other side of the fixingprotrusion 104 and the protrusion 129 located in the center parts of thelong sides, from the first pedestal 127, and is provided near the fixingprotrusion 104 and the protrusion 129. The second pedestal 125 may becoupled to one of the fixing protrusion 104 and the protrusion 129. Thesecond pedestal 125 functions as a pedestal for fixing the circuit board115 to the container 101, on the other side of the fixing protrusion 104and the protrusion 129 from the first pedestal 127.

The outer shape of the container 101 is described as the shape of arectangular-parallelepiped box having a substantially rectangular planarshape and no lid. However, the outer shape of the container 101 is notlimited to this. The planar shape of the outer shape of the container101 may be square, hexagonal, octagonal or the like. In the planar shapeof the outer shape of the container 101, the vertices of the polygon maybe chamfered and one of the sides may be curved. The planar shape insidethe container 101 is not limited to the foregoing shape, either, and maybe another shape. The planar shapes of the outer shape and inside of thecontainer 101 may be similar or not similar to each other.

The circuit board 115 is a multilayer board having a plurality ofthrough-holes or the like formed therein and uses a glass epoxy board.However, the circuit board 115 is not limited to a glass epoxy board andmay be a rigid board on which a plurality of physical quantity sensors,electronic components, connectors and the like can be installed. Forexample, a composite board or a ceramic board may be used.

The circuit board 115 has a second surface 115 r on the side of thebottom wall 112 and a first surface 115 f having a front-back relationwith the second surface 115 r. On the first surface 115 f of the circuitboard 115, a control IC 119 as a processor and acceleration sensors 118x, 118 y, 118 z as physical quantity sensors are installed. On thesecond surface 115 r of the circuit board 115, the connector 116 isinstalled. Although not illustrated or described, other wirings andterminal electrodes or the like may be provided on the circuit board115.

The circuit board 115 has the constricted parts 133, 134, which areformed by constricting the outer edge of the circuit board 115, in acenter part along the X-axis on the long sides of the container 101, asviewed in a plan view. The constricted parts 133, 134 are provided onboth sides along the Y-axis of the circuit board 115, as viewed in aplan view, and are constricted toward the center from the outer edge ofthe circuit board 115. The constricted parts 133, 134 are providedfacing the protrusion 129 and the fixing protrusion 104 of the container101.

The circuit board 115 is inserted in the internal space of the container101, with the second surface 115 r facing the first pedestal 127 and thesecond pedestal 125. The circuit board 115 is supported in the container101 by the first pedestal 127 and the second pedestal 125.

The acceleration sensors 118 x, 118 y, 118 z detecting acceleration as aphysical quantity respectively detect acceleration along one axis.Specifically, the acceleration sensor 118 x is provided upright in sucha way that the front and back surfaces of its package are placed on theX-axis and that a lateral surface faces the first surface 115 f of thecircuit board 115. The acceleration sensor 118 x detects accelerationapplied on the X-axis and outputs a measurement target signalcorresponding to the detected acceleration. The acceleration sensor 118y is provided upright in such a way that the front and back surfaces ofits package are placed on the Y-axis and that a lateral surface facesthe first surface 115 f of the circuit board 115. The accelerationsensor 118 y detects acceleration applied on the Y-axis and outputs ameasurement target signal corresponding to the detected acceleration.The acceleration sensor 118 z is provided in such a way that the frontand back surfaces of its package are placed on the Z-axis and that thefront and back surfaces of the package directly face the first surface115 f of the circuit board 115. The acceleration sensor 118 z detectsacceleration applied on the Z-axis and outputs a measurement targetsignal corresponding to the detected acceleration.

The control IC 119 as a processor is electrically coupled to theacceleration sensors 118 x, 118 y, 118 z via a wiring, not illustrated.The control IC 119 is a MCU (micro controller unit) and includes an A/Dconverter (equivalent to the A/D converter 2 described in the aboveembodiments) to which the measurement target signals outputtedrespectively from the acceleration sensors 118 x, 118 y, 118 z areinputted, the resampling circuit 1 of one of the above embodiments, adigital processing circuit which performs various kinds of conversionand correction on the measurement data outputted from the resamplingcircuit 1 and generates detection data, and a storage unit including anon-volatile memory, or the like. The control IC 119 controls each partof the physical quantity sensor unit 100. The control IC 119 alsogenerates detection data synchronized with an external trigger, based onthe measurement target signals outputted respectively from theacceleration sensors 118 x, 118 y, 118 z, and generates packet dataincluding the detection data. In the storage unit, a program prescribingthe order and content of detecting acceleration, a program for includingthe detection data into the packet data, and accompanying data or thelike are stored. Although not illustrated, a plurality of otherelectronic components or the like may be installed on the circuit board115.

An example of the configuration of the acceleration sensors 118 x, 118y, 118 z will now be described with reference to FIGS. 12 and 13.

FIG. 12 is a perspective view for explaining a schematic configurationof a sensor element for detecting acceleration. FIG. 13 is across-sectional view for explaining an acceleration detector using asensor element for detecting acceleration.

In FIG. 12, an x-axis, a y′-axis, and a z′-axis are shown as three axesorthogonal to each other. An example of using a so-called quartz crystalz plate (z′ plate) sliced out along a plane prescribed by the x-axis andthe y′-axis and processed into the shape of a flat plate and havingpredetermined thickness t on the z′-axis orthogonal to this plane, as abase material, will be described, where the z′-axis is formed by tiltinga z-axis by an angle of rotation ϕ (preferably −5°≤ϕ≤15°) so that a +zside rotates into a −y direction on a y-axis and where the y′-axis isformed by tilting the y-axis by the angle of rotation ϕ so that a +yside rotates into a +z direction on the z-axis, in an orthogonalcoordinate system having the x-axis as an electrical axis, the y-axis asa mechanical axis, and the z-axis as an optical axis of quartz crystalwhich is a piezoelectric material used as a base material of anacceleration sensor. The z′-axis is an axis along a direction in whichgravity acts in the acceleration sensors 118 x, 118 y, 118 z.

First, the configuration of a sensor element 200 detecting accelerationwill be described with reference to FIG. 12. The sensor element 200 hasa substrate structure 201 including a base 210 or the like, anacceleration detection element 270 coupled to the substrate structure201 and detecting a physical quantity, and mass elements 280, 282.

The substrate structure 201 of the sensor element 200 has the base 210,a moving element 214 coupled to the base 210 via a joint 212, a coupler240, and a first support 220, a second support 230, a third support 250,and a fourth support 260 which are coupled to the base 210. The thirdsupport 250 and the fourth support 260 are coupled together on the sidewhere the coupler 240 is arranged.

The substrate structure 201 uses a quartz crystal substrate made up of aquartz crystal z plate (z′ plate) sliced out at a predetermined angle,as described above, from a quartz crystal ore as a piezoelectricmaterial. The quartz crystal substrate is patterned to integrally formthe components as the substrate structure 201. The patterning can use,for example, photolithography or wet etching.

The base 210 is coupled to the moving element 214 via the joint 212 andsupports the moving element 214. The base 210 is coupled to the movingelement 214 via the joint 212, to the coupler 240 located on the sideopposite to the side where the joint 212 of the moving element islocated, to the first support 220 and the second support 230, and to thethird support 250 and the fourth support 260 coupled together on theside of the coupler 240.

The joint 212 is provided between the base 210 and the moving element214 and is coupled to the base 210 and the moving element 214. Thethickness (length along the z′-axis) of the joint 212 is thinner(shorter) than the thickness of the base 210 and the thickness of themoving element 214. The joint 212 is constricted as viewed in across-sectional view from the x-axis. The joint 212 is formed, forexample, as a thin part with a thin thickness by so-called half-etchingof the substrate structure 201 including the joint 212. The joint 212has the function of an axis of rotation along the x-axis as a fulcrum(intermediate hinge) when the moving element 214 is displaced (pivots)about the base 210.

The moving element 214 is coupled to the base 210 via the joint 212. Themoving element 214 is in the shape of a plate and has main surfaces 214a, 214 b having a front-back relation with each other along the z′-axis.The moving element 214 is displaced along the axis (z′-axis)intersecting the main surfaces 214 a, 214 b about the joint 212 as thefulcrum (axis of rotation) in response to acceleration as a physicalquantity applied on the axis (z′-axis) intersecting the main surfaces214 a, 214 b.

The coupler 240 extends in such a way as to surround the moving element214 along the x-axis from the base 210 on the +x side, where the thirdsupport 250, described later, is provided. The coupler 240 is coupled tothe base 210 on the −x side, where the fourth support 260, describedlater, is provided.

The first support 220 and the second support 230 are provided, formingsymmetry about the acceleration detection element 270. The third support250 and the fourth support 260 are provided, forming symmetry about theacceleration detection element 270. At the first support 220, the secondsupport 230, the third support 250, and the fourth support 260, thesubstrate structure 201 is supported to a fixing target element.

The acceleration detection element 270 is coupled to the base 210 andthe moving element 214. In other words, the acceleration detectionelement 270 is provided extending over the base 210 and the movingelement 214. The acceleration detection element 270 has vibrating beams271 a, 271 b as vibrators, and a first base 272 a and a second base 272b. In the acceleration detection element 270 having the first base 272 aand the second base 272 b coupled to the base 210, for example, as themoving element 214 is displaced in response to a physical quantity, astress is generated in the vibrating beams 271 a, 271 b and physicalquantity detection information generated in the vibrating beams 271 a,271 b changes. In other words, the vibration frequency (resonancefrequency) of the vibrating beams 271 a, 271 b changes. The accelerationdetection element 270 in this embodiment is a dual tuning fork element(dual tuning fork-type vibration element) having the two vibrating beams271 a, 271 b, the first base 272 a, and the second base 272 b. Thevibrating beams 271 a, 271 b as vibrators may also be referred to asvibrating arms, vibrating beams, or columnar beams or the like.

For the acceleration detection element 270, a quartz crystal substratemade of a quartz crystal z plate (z′ plate) sliced out at apredetermined angle from a quartz crystal ore or the like as apiezoelectric material, similarly to the foregoing substrate structure201, is used. The acceleration detection element 270 is formed of thequartz crystal substrate patterned by photolithography or etching. Thus,the vibrating beams 271 a, 271 b, the first base 272 a, and the secondbase 272 b can be integrally formed.

The material of the acceleration detection element 270 is not limited tothe quartz crystal substrate. As the material of the accelerationdetection element 270, for example, a piezoelectric material such aslithium tantalate (LiTaO₃), lithium tetraborate (Li₂B₄O₇), lithiumniobate (LiNbO₃), lead zirconate titanate (PZT), zinc oxide (ZnO), oraluminum nitride (AlN), or a semiconductor material such as siliconhaving a piezoelectric (piezoelectric material) coating such as zincoxide (ZnO) or aluminum nitride (AlN) can be used. In this case, thesame material may be preferably used for the substrate structure 201 andthe acceleration detection element 270.

Although not illustrated or described, the acceleration detectionelement 270 may be provided with an extraction electrode or anexcitation electrode.

The mass elements 280, 282 are provided on the main surface 214 a of themoving element 214 and on the main surface 214 b, which is the back facein the front-back relation with the main surface 214 a. Morespecifically, the mass elements 280, 282 are provided over the mainsurfaces 214 a, 214 b via a mass joining member (not illustrated). Thematerial of the mass elements 280, 282 can be, for example, a metal suchas copper (Cu) or gold (Au).

In this embodiment, the vibrator of the acceleration detection element270 is formed of a dual tuning fork vibrator (dual tuning fork-typevibration element) made up of the two columnar beams of the vibratingbeams 271 a, 271 b. However, the vibrator can be made up of one columnarbeam (single beam).

Next, the configuration of an acceleration detector 300 using theforegoing sensor element 200 for detecting acceleration will bedescribed with reference to FIG. 13.

As shown in FIG. 13, the foregoing sensor element 200 is installed inthe acceleration detector 300. The acceleration detector 300 has thesensor element 200 and a package 310. The package 310 has a package base320 and a lid 330. The sensor element 200 is accommodated in the package310 of the acceleration detector 300. Specifically, the sensor element200 is accommodated in a space 311 provided by the package base 320 andthe lid 330 coupled to each other.

The package base 320 has a recess 321. The sensor element 200 isprovided inside the recess 321. The shape of the package base 320 is notparticularly limited, provided that the sensor element 200 can beaccommodated inside the recess 321. The package base 320 in thisembodiment can use a material such as ceramic, quartz crystal, glass orsilicon.

The package base 320 has a step 323 protruding toward the lid 330 froman inner bottom surface 322, which is a bottom surface on the inner sideof the recess of the package base 320. The step 323 is provided, forexample, along the inner wall of the recess 321. A plurality of internalterminals 340 b is provided on the step 323.

The internal terminal 340 b is provided facing a position that overlapsa fixed part coupling terminal 379 b provided at a fixed part of each ofthe first support 220, the second support 230, the third support 250,and the fourth support 260 of the sensor element 200, as viewed in aplan view. The internal terminal 340 b is electrically coupled to thefixed part coupling terminal 379 b, for example, using a siliconeresin-based conductive adhesive 343 containing a conductive materialsuch as a metal filler. The sensor element 200 is thus loaded in thepackage base 320 and accommodated inside the package 310.

In the package base 320, an external terminal 344 used to load thepackage on an external member is provided on an outer bottom surface324, which is a surface opposite to the inner bottom surface 322. Theexternal terminal 344 is electrically coupled to the internal terminal340 b via an internal wiring, not illustrated.

The internal terminal 340 b and the external terminal 344 are made upof, for example, a multilayer metal film including a metalized layer oftungsten (W) or the like coated with nickel (Ni), gold (Au) or the likeby plating or the like.

In the package base 320, a seal 350 sealing the inside of the package310 is provided at a bottom part of the recess 321. The seal 350 isprovided inside a penetration hole 325 formed in the package base 320.The penetration hole 325 penetrates the package base 320 from the outerbottom surface 324 to the inner bottom surface 322. In the example shownin FIG. 13, the penetration hole 325 has a stepped shape with the holediameter on the side of the outer bottom surface 324 being larger thanthe hole diameter on the side of the inner bottom surface 322. The seal350 is formed, for example, by arranging a sealant made up of an alloyof gold (Au) and germanium (Ge), or a solder or the like in thepenetration hole 325, and heating and melting and then solidifying thesealant. The seal 350 is provided to airtightly seal the inside of thepackage 310.

The lid 330 is provided covering the recess 321 of the package base 320.The lid 330 is, for example, in the shape of a plate. For the lid 330,for example, the same material as the package base 320, an alloy of iron(Fe) and nickel (Ni), or a metal such as stainless steel can be used.The lid 330 is joined to the package base 320 via a lid joining member332. As the lid joining member 332, for example, a seam ring,low-melting glass, inorganic adhesive or the like can be used.

After the lid 330 is joined to the package base 320, the sealant isarranged in the penetration hole 325 in the state where the pressureinside the package 310 is reduced (the degree of vacuum is high), andthe sealant is heated and melted and subsequently solidified to providethe seal 350. Thus, the inside of the package 310 can be sealedairtightly. The inside of the package 310 may be filled with an inertgas such as nitrogen, helium, or argon.

In the acceleration detector 300, when a drive signal is provided to theexcitation electrode of the sensor element 200 via the external terminal344, the internal terminal 340 b, the fixed part coupling terminal 379 bor the like, the vibrating beams 271 a, 271 b of the sensor element 200vibrate at a predetermined frequency. The acceleration detector 300outputs the resonance frequency of the sensor element 200 changingaccording to the applied acceleration, as an output signal. Theacceleration detector 300 can be used as the acceleration sensors 118 x,118 y, 118 z of the physical quantity sensor unit 100. The accelerationsensors 118 x, 118 y, 118 z respectively output a measurement targetsignal with a frequency corresponding to the applied acceleration.

The physical quantity sensor unit 100 of the embodiment described aboveincludes the resampling circuit 1 configured to reduce a periodic noisegenerated in resampled measurement data, and therefore can detect aphysical quantity with high accuracy.

Up to this point, the physical quantity sensor unit 100 having theacceleration sensors 118 x, 118 y, 118 z as physical quantity sensors isdescribed as an example. However, a physical quantity sensor unit havinga physical quantity sensor which detects at least one of mass, angularvelocity, angular acceleration, electrostatic capacitance, andtemperature as a physical quantity may be employed.

For a mass sensor which detects mass as a physical quantity, a quartzcrystal vibrator microbalance method (QCM or quartz crystalmicrobalance) is known as a technique for measuring a very small masschange. Such a mass sensor utilizes the fact that the oscillationfrequency of the quartz crystal vibrator decreases when the mass ofmatter adhering to the electrode surface of the quartz crystal vibratorincreases, whereas the oscillation frequency increases when the mass ofthe adhering matter decreases. The detection sensitivity of the masssensor as described above can be calculated by the Sauerbrey equation.For example, for an AT-cut quartz crystal vibrator with a fundamentalfrequency of 27 MHz, a decrease in frequency of 1 Hz corresponds to anincrease in mass of 0.62 ng/cm² on the electrode surface.

An angular velocity sensor which detects angular velocity or angularacceleration as a physical quantity detects angular velocity, utilizingthe fact that an object rotating at a constant angular velocity ωappears to be rotating at an angular velocity of “ω-Ω” when the objectis observed from an observation point rotating at an angular velocity Ω.Such an angular velocity sensor utilizes the fact that when a sensorelement receives an angular velocity in the state where a disc-shapedmass is electrostatically driven using an electrode and thus causes awave having a natural frequency to circle, the apparent resonancefrequency observed from the electrode changes. The angular velocitysensor as described above has no theoretical limitation on thebandwidth. Therefore, for example, higher accuracy of a technique forfrequency measurement or a technique for nonlinear correction directlyleads to higher detection sensitivity.

An electrostatic capacitance sensor which detects electrostaticcapacitance as a physical quantity causes RC oscillation using areference resistance and a measurement target electrostatic capacitanceand measures the oscillation frequency, and thus can measure themeasurement target electrostatic capacitance. The electrostaticcapacitance sensor utilizes the fact that when the measurement targetelectrostatic capacitance changes, a time constant provided by the RCchanges and hence the oscillation frequency shifts. Also, theelectrostatic capacitance sensor may be provided with a referenceelectrostatic capacitance separate from the measurement targetelectrostatic capacitance and thus may have a mechanism which causes RCoscillation using the reference resistance and the referenceelectrostatic capacitance, defines its frequency as a referenceoscillation frequency, and detects the difference between the foregoingoscillation frequency and the reference oscillation frequency. This caneliminate various error factors.

A temperature sensor which detects temperature as a physical quantitycauses RC oscillation using a thermistor and a reference electrostaticcapacitance and measures the oscillation frequency, and thus can measuretemperature. The temperature sensor utilizes the fact that when theresistance value of the thermistor changes due to temperatures, a timeconstant provided by the RC changes and hence the oscillation frequencyshifts. Also, the temperature sensor may be provided with a referenceresistor separate from the thermistor and thus may have a mechanismwhich causes RC oscillation using the reference resistance and thereference electrostatic capacitance, defines its frequency as areference oscillation frequency, and detects the difference between theforegoing oscillation frequency and the reference oscillation frequency.This can eliminate various error factors.

The physical quantity sensor unit 100 having the physical quantitysensors for detecting various physical quantities as described aboveincludes the resampling circuit 1 configured to reduce a periodic noisegenerated in resampled measurement data and therefore can detect aphysical quantity with high accuracy.

3. Inertial Measurement Unit (IMU)

An inertial measurement unit according to this embodiment includes aphysical quantity sensor which detects at least one of acceleration andangular velocity and which outputs a measurement target signal, a signalprocessing circuit which includes the resampling circuit 1 according tothe foregoing embodiments and which processes a signal outputted fromthe physical quantity sensor, and a communication circuit whichtransmits inertial data resulting from the processing by the signalprocessing circuit, to outside. The inertial measurement unit transmitsthe inertial data synchronously with an external trigger supplied froman arithmetic processing device (host).

The inertial measurement unit of this embodiment may have, for example,a structure similar to the physical quantity sensor unit 100 except thatthe components installed on the circuit board 115 are different. FIG. 14is a perspective exterior view showing the configuration of a circuitboard of an inertial measurement unit 400 of this embodiment. In FIG.14, components similar to those in FIG. 11 are denoted by the samereference signs and will not be described repeatedly.

As shown in FIG. 14, the circuit board 115 provided in the inertialmeasurement unit 400 of this embodiment is divided into a first areaAL1, a second area AL2, and a coupling area AL3 located between thefirst area AL1 and the second area AL2. On a first surface of the secondarea AL2 of the circuit board 115, three acceleration sensors 118 x, 118y, 118 z configured to detect acceleration on one axis each and anangular velocity sensor 117 configured to detect angular velocity onthree axes are installed. The angular velocity sensor 117, as a singledevice, can detect angular velocity on an X-axis, a Y-axis, and aZ-axis, that is, on three axes. The angular velocity sensor 117 may use,for example, a vibration gyro sensor made up of a silicon substrateprocessed by a MEMS technique so as to detect angular velocity, based ona Coriolis force applied to a vibrating object. Also, a control IC 119 gis installed on a first surface of the first area AL1 of the circuitboard 115, and a plug-type (male) connector (not illustrated) isinstalled on a second surface having a front-back relation with thefirst surface of the first area AL1 of the circuit board 115.

The control IC 119 g as a processor is electrically coupled to theacceleration sensors 118 x, 118 y, 118 z and the angular velocity sensor117 via a wiring, not illustrated. The control IC 119 g is a MCU andincludes a signal processing circuit which processes an accelerationsignal outputted from the acceleration sensors 118 x, 118 y, 118 z andan angular velocity signal outputted from the angular velocity sensor117, a communication circuit which transmits inertial data resultingfrom the processing by the signal processing circuit, to outside, and astorage unit including a non-volatile memory, or the like. The signalprocessing circuit includes an A/D converter (equivalent to the A/Dconverter 2 described in the foregoing embodiments) to which anacceleration signal or an angular velocity signal as a measurementtarget signal is inputted, the resampling circuit 1 of one of theforegoing embodiments, and a digital processing circuit which performsvarious kinds of conversion and correction on measurement data outputtedfrom the resampling circuit 1 and generates inertial data, or the like.The control IC 119 g controls each part of the physical quantity sensorunit 100, generates inertial data synchronized with an external trigger,based on the acceleration signals outputted respectively from theacceleration sensors 118 x, 118 y, 118 z and the angular velocity signaloutputted from the angular velocity sensor 117, and generates packetdata including the inertial data. In the storage unit, a programprescribing the order and content of detecting acceleration or angularvelocity, a program for including the inertial data into the packetdata, and accompanying data or the like are stored. Although notillustrated, a plurality of other electronic components or the like maybe installed on the circuit board 115.

With such a configuration, the inertial measurement unit 400 can detect,for example, an attitude and behavior (amount of inertial motion) of avehicle (installation target device) such as an automobile, agriculturalmachine (farm machine), construction machine (building machine), robot,and drone. The inertial measurement unit 400 functions as a so-calledsix-axis motion sensor having the acceleration sensors 118 x, 118 y, 118z for three axes and the angular velocity sensor 117 for three axes.

The inertial measurement unit 400 of this embodiment described aboveincludes the resampling circuit 1 configured to reduce a periodic noisegenerated in resampled measurement data and therefore can generateinertial data with high accuracy.

Although the inertial measurement unit 400 is described above as havingan acceleration sensor and an angular velocity sensor, the inertialmeasurement unit 400 may have an angular velocity sensor without havingan acceleration sensor, or may have an acceleration sensor withouthaving an angular velocity sensor.

4. Structure Monitoring Device (SHM or Structure Health Monitoring)

FIG. 15 shows the configuration of a structure monitoring deviceaccording to this embodiment. As shown in FIG. 15, a structuremonitoring device 500 according to this embodiment has a physicalquantity sensor unit 510 which has the same functions as the physicalquantity sensor unit 100 of the foregoing embodiments and which isinstalled in a structure 590 as a monitoring target. The physicalquantity sensor unit 510 includes a transmitter 511 which transmits adetection signal. The transmitter 511 may be implemented as acommunication module and antenna separate from the physical quantitysensor unit 510.

The physical quantity sensor unit 510 is coupled, for example, to amonitoring computer 570 via a wireless or wired communication network580. The monitoring computer 570 has a receiver 520 coupled to thephysical quantity sensor unit 510 via the communication network 580, anda calculator 530 which calculates an angle of inclination of thestructure 590, based on a received signal outputted from the receiver520.

The calculator 530 in this embodiment is implemented by an ASIC(application-specific integrated circuit) or FPGA (field-programmablegate array) or the like installed in a monitoring computer 570. However,the calculator 530 may be a processor such as a CPU (central processingunit), and the processor may arithmetically process a program stored inan IC memory 531, thus implementing a software-based configuration. Themonitoring computer 570 can accept various operation inputs made by anoperator via a keyboard 540 and display the result of arithmeticprocessing on a touch panel 550.

The structure monitoring device 500 of this embodiment monitors theinclination of the structure 590, using the physical quantity sensorunit 510 having the same functions as the physical quantity sensor unit100 of the foregoing embodiments. Therefore, the structure monitoringdevice 500 can utilize the highly accurate detection of a physicalquantity (acceleration, angular velocity or the like), which is anadvantageous effect of the physical quantity sensor unit 100. Thus, thestructure monitoring device 500 can accurately detect the inclination ofthe structure 590 as a monitoring target and can improve the monitoringquality for the structure 590.

The application of the present disclosure is not limited to theembodiments. Various changes can be made without departing from thescope and spirit of the present disclosure.

For example, while the resampling circuit 1 in the embodimentscalculates the measurement data by linear approximation based on therelation between the first time interval and the second time interval,and a plurality of AD data, the resampling circuit 1 may calculate themeasurement data by approximation other than linear approximation, suchas by curve approximation.

Also, for example, while the resampling circuit 1 of the firstembodiment or the second embodiment carries out approximation based ontwo AD data updated at two successive edges of the AD clock and theresampling circuit 1 of the third embodiment or the fourth embodimentcarries out approximation based on three AD data updated at threesuccessive edges of the AD clock, the resampling circuit 1 may carry outapproximation based on four or more AD data updated at four or moresuccessive edges of the AD clock.

The foregoing embodiments and modifications are simply examples and arenot limiting. For example, the embodiments and modifications can besuitably combined together.

The present disclosure includes a configuration substantially similar toany of the configurations described in the embodiments (for example, aconfiguration having the same function, method, and result, or aconfiguration having the same object and effect). The present disclosurealso includes a configuration replacing a non-essential element of anyof the configurations described in the embodiments. The presentdisclosure also includes a configuration having the same advantageouseffect or achieving the same object as any of the configurationsdescribed in the embodiments. The present disclosure also includes aconfiguration including the related-art technique added to any of theconfigurations described in the embodiments.

What is claimed is:
 1. A resampling circuit converting first dataupdated synchronously with a first clock signal into second data updatedsynchronously with a second clock signal asynchronous with the firstclock signal and outputting the second data, the resampling circuitmeasuring a first time interval, which is a time interval between aplurality of successive edges of the first clock signal, and a secondtime interval, which is a time interval between one of the plurality ofedges of the first clock signal and an edge of the second clock signal,with a third clock signal having a higher frequency than the first clocksignal and the second clock signal, the resampling circuit calculatingand outputting the second data updated at the edge of the second clocksignal, based on the first time interval and the second time interval,and a plurality of the first data updated at the plurality of edges ofthe first clock signal.
 2. The resampling circuit according to claim 1,wherein a first edge of the plurality of edges of the first clock signaloccurs before the edge of the second clock signal, a second edge of theplurality of edges of the first clock signal occurs after the edge ofthe second clock signal, and the second time interval is a time intervalbetween the first edge and the edge of the second clock signal.
 3. Theresampling circuit according to claim 1, wherein a first edge of theplurality of edges of the first clock signal occurs before the edge ofthe second clock signal, a second edge of the plurality of edges of thefirst clock signal occurs after the first edge and before the edge ofthe second clock signal, and the second time interval is a time intervalbetween the second edge and the edge of the second clock signal.
 4. Theresampling circuit according to claim 1, wherein the second data updatedat the edge of the second clock signal is calculated by approximationbased on a relation between the first time interval and the second timeinterval, and a plurality of the first data updated at the plurality ofedges of the first clock signal.
 5. The resampling circuit according toclaim 4, wherein the approximation is linear approximation.
 6. Theresampling circuit according to claim 1, comprising a low-pass filterwhich outputs the first data, wherein a cutoff frequency of the low-passfilter is lower than a Nyquist frequency of the second clock signal. 7.The resampling circuit according to claim 1, wherein the first clocksignal is a sampling clock in A/D conversion.
 8. The resampling circuitaccording to claim 1, wherein the second clock signal is a triggersignal inputted from outside to the resampling circuit.
 9. A physicalquantity sensor unit comprising: the resampling circuit according toclaim 1; and a physical quantity sensor.
 10. The physical quantitysensor unit according to claim 9, wherein the physical quantity sensordetects at least one of acceleration and angular velocity.
 11. Astructure monitoring device comprising: the physical quantity sensorunit according to claim 10; a receiver which receives a detection signalfrom the physical quantity sensor unit installed on a structure; and acalculator which calculates an angle of inclination of the structure,based on a signal outputted from the receiver.
 12. An inertialmeasurement unit comprising: a physical quantity sensor which detects atleast one of acceleration and angular velocity; a signal processingcircuit which includes the resampling circuit according to claim 1 andprocesses a signal outputted from the physical quantity sensor; and acommunication circuit which transmits inertial data resulting from theprocessing by the signal processing circuit to outside.